Cushion handle for percussive tools



March 10, 1953 WALLERSTEIN, JR 2,630,784

CUSHION HANDLE FOR PERCUSSIVE TOOLS Filed June 20, 1949 ummv Patented Mar. 10, 1953 2,630,784 CUSHION HANDLE FOR PERCUSSIVE TOOLS Leon Wallerstein, Jr., Erie, Pa., assignor to Lord Manufacturing Company, Erie, Pan, a. corporation of Pennsylvania Application June 20, 1949, Serial No. 100,218

3 Claims. (01. 12136) ural frequency on the tool less than /2 times the disturbing frequency created in thetool so the handle tends to stay normally fixed in space and the sensible vibration transmitted to the operator is decreased. Advantages include preloading so the operator mustexert the proper hold-down force in order to obtain any benefit from the vibration isolating support, a torsion spring support in which the handle support is resiliently hinged about an axis transverse to the direction of the operating force so advantage can be taken of the moment of inertia of the handle to obtain a low natural frequency of the handle, and a handle mounting which provides a stable connection so that the tool can be handled as though the handle were firmly connected. Further objects and advantages appear in the specification and claims.

In the drawing, Fig. 1 is a side elevation of a jack hammer; Fig. 2 is an enlarged section; and Fig. 3 is a top view partly broken away.

I indicates the cylinder which houses the actuating parts, 2 indicates the front head which applies the percussive force, for example to a drill steel 3 carried thereby, and 4 indicates the back head at the upper end of the cylinder. The foregoing sufficiently identifies the jack hammer which is, or may be, of common construction.

At one side of the axis or line of action of the percussive force is a transverse hinge pin 6 fixed in ears 1 projecting from the back head. The projecting ends of the hinge pin are locked to center pins 8 of tube form rubber mountings 8a having outer shells 9 locked in sockets ID in spaced arms ii at one end of a handle 12. The handle has at its other end spaced arms I3 receiving a handle bar [4 which projects on each side to provide hand grips.

When the jack hammer is not in use, a cross bar connecting the ends of the arms II is urged against a stop surface 16 on the ears 1 with a force determined by the original pre-loading of the rubber bushings l8 bonded or locked to the center pins and outer shells of the tube form mountings 8a. The pre-loading is efiected by relative rotation of the center pins and outer shells so that the rubber exerts a force tending to pivot the handle upward, or in a clockwise direction as viewed in Fig. 2. The stop surface l6 prevents upward movement of the handle. The handle is therefore held against the stop surface with a. force equal to the pre-loading force. This provides an effectively rigid connection between the handle and tool when the tool is not in use.

Preferably the pre-loading is such that it can be overcome only after the operator exerts the proper hold-down force on the handle necessary to secure proper operation of the tool. For example, in a typical jack hammer which weighs pounds and operates at 1800 strokes a minute, it is desirable that the drill steel 3 be held against the work with a force of from to pounds. For such a tool, the pre-loading will require a hold-down force of from 100 to 150 pounds on the handle bar 14 to move the cross bar l5 clear of the stop surface [6.

Once the cross bar [5 is clear of the stop surface IS, the handle is resiliently supported on the jack hammer by the tube form mountings 8a. Unless the resilient support of the handle is such that the natural frequency of vibration of the handle relative to the tool is less than /2 times the frequency of the disturbing vibration from the percussive forces, the operator will obtain no reduction in the sensible vibration at the handle grips. For the typical jack hammer men tioned above, a handle natural frequency of 720 cycles per minute results in isolation of about 75% of the sensible vibration which would otherwise reach the hand grips. A handle natural frequency of 1272 cycles per minute would result in no reduction in the sensible vibration transmitted to the handle grips.

The natural frequency of the handle relative to the tool is not dependent upon the weight of the tool nor the hold-down force required to hold the tool against the work. The natural frequency is determined by the mass or moment of inertia of the handle and by the spring rate of the handle mountings. For the mountings shown where the handle support uses torsion springs, the natural frequency depends upon the moment of inertia of the handle about the hinge pin 6 and the spring rate in pound inches per radian. Since the moment of inertia of the handle increases as the square of the length of the handle and as the first power of the weight of the handle, the ofiset hinge pin 6 results in a lighter handle. This decreases the dead weight.

If the operator relaxes the hold-down force on the hand grips to less than the pre-loading, the cross bar l5 engages the stop surface I6 and all of the vibration comes through the hand grips. The pre-loading accordingly serves as a warning to the operator that too little hold-down force is being applied.

The reduction in sensible vibration at the hand grips is important. Vibration in time produces fatigue and a marked reduction in the efiiciency of the operator. Elimination of vibration not only is more comfortable but it is essential if the tool is to be used for extended periods of time.

What I claim as new is: 1. In a jack hammer or similar percussive tool, a handle for applying a hold-down force to the loading force, the stiffness of the spring when pre-loaded being such that the natural frequency of the handle on the tool is less than /2 times 1 the frequency of the vibration from the percussive forces.

2. In a jack hammer or similar percussive tool, a handle for applying a hold-down force to the tool along the axis of the percussive forces, a torsion spring mounting for the handle ofiset to one side and crosswise of the axis of the holddoWn force, the spring being preloaded to exert a force on the handle opposing the hold-down force, and a stop against which the handle is held by the preloading force until overcome by the hold-down force, the stiffness of the spring when pre-loaded being such that the natural frequency of the handle relative to the tool is less than /2 times the frequency of the vibration from the percussive forces.

3. In a jack hammer or similar percussive tool, a handle for applying a hold-down force to the tool along the axis of the percussive forces, a torsion spring mounting for the handle offset to one side and crosswise of the axis of the holddown force, the spring being preloaded to exert a force on the handle opposing the hold-down force, and a stop against which the handle is held by the preloading force until overcome by the hold-down force, the stiffness of the spring when pre-loaded being such that the natural frequency of the handle relative to the tool is less than %\/2 times the frequency of the vibration from the percussive forces, said torsion spring mounting comprising a bushing of rubber surrounding the torsion axis and having inner and outer surfaces, one looked to the tool and the other locked to the handle.

LEON WALLERSTEIN, JR.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,649,730 Prellwitz Nov. 15, 1927 2,062,817 Noble Dec. 1, 1936 FOREIGN PATENTS Number Country Date 122,752 Austria May 11, 1931 

